linux-kernel - [PATCH tip/core/rcu 2/2] rcu: Trace callback acceleration

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Date:	Sat, 26 Jan 2013 16:18:21 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	mingo@...e.hu, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...ymtl.ca,
	josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, edumazet@...gle.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 2/2] rcu: Trace callback acceleration

From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>

This commit adds event tracing for callback acceleration to allow better
tracking of callbacks through the system.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/trace/events/rcu.h |    6 ++++--
 kernel/rcutree.c           |    6 ++++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index d4f559b..5678114 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -44,8 +44,10 @@ TRACE_EVENT(rcu_utilization,
  * of a new grace period or the end of an old grace period ("cpustart"
  * and "cpuend", respectively), a CPU passing through a quiescent
  * state ("cpuqs"), a CPU coming online or going offline ("cpuonl"
- * and "cpuofl", respectively), and a CPU being kicked for being too
- * long in dyntick-idle mode ("kick").
+ * and "cpuofl", respectively), a CPU being kicked for being too
+ * long in dyntick-idle mode ("kick"), a CPU accelerating its new
+ * callbacks to RCU_NEXT_READY_TAIL ("AccReadyCB"), and a CPU
+ * accelerating its new callbacks to RCU_WAIT_TAIL ("AccWaitCB").
  */
 TRACE_EVENT(rcu_grace_period,
 
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index ac6a75d..e9dce4f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1168,6 +1168,12 @@ static void rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
 		rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
 		rdp->nxtcompleted[i] = c;
 	}
+
+	/* Trace depending on how much we were able to accelerate. */
+	if (!*rdp->nxttail[RCU_WAIT_TAIL])
+		trace_rcu_grace_period(rsp->name, rdp->gpnum, "AccWaitCB");
+	else
+		trace_rcu_grace_period(rsp->name, rdp->gpnum, "AccReadyCB");
 }
 
 /*
-- 
1.7.8

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